This is a national stage entry PCT/JP99/03225, international filing date Jun. 17, 1999.
The present invention relates to a spatial light modulating device which uses a spatial light modulator, which is an element for generating a particular modulation in a cross-section of a light beam, and to a spatial light modulating method which uses the spatial light modulator.
A spatial light modulating device is used for optical information processing and computer-generated holograms (CGH). Especially, a spatial light modulating device of a type, which prepares signal images according to electric addresses, is very useful because this type of spatial light modulating device can easily prepare those signal images. A device that can efficiently perform phase modulation is required for the above-described usage.
A device that employs a transmission type liquid crystal element can be considered as an example of this type of spatial light modulating device. Such a device has a merit of being purchasable at a relatively low price. However, such devices have been unable to achieve a phase modulation amount of greater than 2xcfx80, which is required for computer-generated holograms and the like.
In an example of another device that is capable of performing electric addressing is a spatial light modulating device that employs an optically-addressed type spatial light modulator and that uses an electrically-addressed type element for generating write light that will fall incident on the optically-addressed type spatial light modulator. For example, Technical Report of the Institute of Electronics, Information and Communication Engineers, (1997-10) p95-p99, discloses a spatial light modulating device that uses a transmission type liquid crystal element as an electrically-addressed type element and an optically-addressed type parallel-aligned nematic-liquid-crystal spatial light modulator (PAL-SLM) as an optically-addressed type spatial light modulator. In this device, a relay lens is disposed between the transmission type liquid crystal element and the optically-addressed type parallel-aligned nematic-liquid-crystal spatial light modulator. Write light from the transmission type liquid crystal element passes through the relay lens to reach the optically-addressed type PAL-SLM. It is possible to attain phase modulation of 2xcfx80 or greater. Because phase-only modulation can be attained, it is also possible to attain high diffraction efficiency.
There is known another method, other than using a relay lens, to transmit write light from a transmission type liquid crystal element to an optically-addressed type spatial light modulator. In this method, the output end of the transmission type liquid crystal element and the write light input end of the optically-addressed type spatial light modulator are both configured from fiber optic plates, and these two fiber optic plates are optically connected. Alternatively, the output end of the transmission type liquid crystal element and the write light input end of the optically-addressed type spatial light modulator are configured from a single fiber optic plate (Japanese Patent Application Publication No. HEI-7-72503).
However, in the case of the above-described two spatial light modulating devices, a signal component that is generated as a result of a pixel structure of the transmission type liquid crystal element is not erased. There is a problem in that a signal image to be transmitted receives influences from this signal component.
It is an objective of the present invention to overcome the above-described problem and provide a spatial light modulating device and a spatial light modulating method, which transmits, by using write light, a signal image from an electrically-addressed type element, which has a pixel structure, to an optically-addressed type spatial light modulator, and which is capable of erasing the signal component caused by the pixel structure and suppressing degrades in the signal image.
In order to solve the above-described problems, a spatial light modulating device of the present invention comprises: an electrically-addressed type spatial light modulator, which has a pixel structure where a plurality of pixels are arranged at a predetermined pitch P, and which is addressed by electric signals representing information to be written, thereby modulating incident write light; an optically-addressed type spatial light modulator, which has an optical addressing layer and a light modulation layer between a pair of transparent electrodes and which modulates read light incident to the light modulation layer by the write light incident to the optical addressing layer; and an optical connecting element which guides the write light, which has been modulated by the electrically-addressed type spatial light modulator and which has been outputted therefrom, to the optical addressing layer of the optically-addressed type spatial light modulator, the optical connecting element having a predetermined critical transfer spatial frequency "ugr"c, the value of the critical transfer spatial frequency "ugr"c and the value of a pixel structure spatial frequency 1/P of the pixel structure in the electrically-addressed type spatial light modulator satisfying the following relationship: "ugr"c less than 1/P.
According to the spatial light modulating device described above, the relationship of "ugr"c less than 1/P is established between the critical transfer spatial frequency "ugr"c and the pixel structure spatial frequency 1/P. Accordingly, it is possible to erase, from write light that reaches the optically-addressed spatial light modulator, a signal component that is caused by the pixel structure of the electrically-addressed type spatial light modulator.
It is preferable that the value of the critical transfer spatial frequency "ugr"c of the optical connecting element and the value of the pixel structure spatial frequency 1/P further satisfy the relationship of 1/2P less than "ugr"c. The spatial frequency of a signal image generated by the electrically-addressed type element is limited to be lower than or equal to the maximum spatial frequency 1/2P that is determined dependently on the pitch P of the pixel structure. By further applying the condition of 1/2P less than "ugr"c to the critical transfer spatial frequency "ugr"c and the pixel structure spatial frequency 1/P, it is possible to transmit the write light without any degradation over the entire range of the spatial frequencies included in the signal image. It is therefore possible to attain a spatial light modulating device that can erase the signal component caused by the pixel structure and that can generate no degradation in the signal image.
In the case where the optically-addressed type spatial light modulator has sensitivity characteristic to write light wavelength, the sensitivity characteristic has a predetermined sensitivity to a predetermined wavelength xcex and has another sensitivity to a wavelength other than the predetermined wavelength xcex, and the predetermined sensitivity is higher than the other sensitivity, the value of the critical transfer spatial frequency "ugr"c of the optical connecting element is preferably determined based on a numerical aperture NA of the optical connecting element and the predetermined wavelength xcex. Because the value of the critical transfer spatial frequency "ugr"c is determined based on the numerical aperture NA of the optical connecting element and the predetermined wavelength xcex that mainly contributes to the modulation in the optically-addressed type spatial light modulator and because the thus determined critical transfer spatial frequency "ugr"c satisfies the relationship of 1/2P less than "ugr"c less than 1/P, it is possible to attain an efficient spatial light modulating device whose output plane has very little influence from the pixel structure. The predetermined frequency xcex may be a wavelength region having a predetermined wavelength width.
It is preferable that the optical connecting element includes a relay lens that has a numerical aperture NAL at a side of the electrically-addressed type spatial light modulator, the value of the critical transfer spatial frequency "ugr"c being equal to NAL/xcex.
The optical connecting element may include a light transmission layer and a fiber optical plate which are connected with each other, the light transmission layer being connected to the electrically-addressed type spatial light modulator, the fiber optical plate being connected to the optically-addressed type spatial light modulator, the fiber optical plate having a numerical aperture NAFOP, the light transmission layer having a thickness d and having a predetermined refractive index nG to the predetermined wavelength xcex, the value of the critical transfer spatial frequency "ugr"c being substantially equal to nG/(dxc2x7NAFOP).
According to another aspect, a spatial light modulating device of the present invention comprises: an electrically-addressed type spatial light modulator, which has a pixel structure where a plurality of pixels are arranged at a predetermined pitch P, and which is addressed by electric signals representing information to be written, thereby modulating incident write light; a relay lens for transferring the write light outputted from the electrically-addressed type spatial light modulator; and an optically-addressed type spatial light modulator, which has an optical addressing layer and a light modulation layer between a pair of transparent electrodes and which modulates read light by the write light outputted from the electrically-addressed type spatial light modulator, the optically-addressed type spatial light modulator having sensitivity characteristic to write light wavelength, the sensitivity characteristic having a predetermined sensitivity to a predetermined wavelength xcex and having another sensitivity to a wavelength other than the predetermined wavelength xcex, the predetermined sensitivity being higher than the other sensitivity, the relay lens having a numerical aperture NAL at a side of the electrically-addressed type element, the value of the numerical aperture NAL, the predetermined pitch P of the pixel structure in the electrically-addressed type spatial light modulator, and the predetermined wavelength xcex of the optically-addressed type spatial light modulator satisfying the following relationship: NAL/xcex less than 1/P.
Because the numerical aperture NAL of the relay lens satisfies the relationship of NAL/xcex less than 1/P for the predetermined wavelength that mainly contributes to the modulation in the optically-addressed type spatial light modulator, it is possible to attain an efficient spatial light modulating device whose output plane has very little influence from the pixel structure. The predetermined frequency xcex may be a wavelength region having a predetermined wavelength width.
It is preferable that the value of the numerical aperture NAL, at a side of the electrically-addressed type element, of the relay lens, the predetermined pitch P of the pixel structure in the electrically-addressed type element, and the predetermined wavelength xcex satisfy the following relationship: NAL/xcex greater than 1/2P. Because the numerical aperture NAL of the relay lens further satisfies the relationship of NAL/xcex greater than 1/2P for the predetermined wavelength xcex or the predetermined wavelength region xcex that mainly contributes to the modulation in the optically-addressed type spatial light modulator, it is possible to attain an efficient spatial light modulating device whose output plane has substantially no degradation in the signal image.
The electrically-addressed type spatial light modulator may preferably include a transmission type liquid crystal element. By using a transmission type liquid crystal element as the electrically-addressed type element, it is possible to produce a write light that bears thereon signal images with little degradation.
The optically-addressed type spatial light modulator may preferably include an optically-addressed type spatial light modulator that uses a photoconductive layer as the optical addressing layer and that uses a liquid crystal layer as the light modulation layer. By using an optically-addressed type spatial light modulator that uses a photoconductive layer as the optical addressing layer and that uses a liquid crystal layer as the light modulation layer, it is possible to attain high diffraction efficiency.
According to another aspect, a spatial light modulating device of the present invention comprises: an electrically-addressed type spatial light modulator, which has a pixel structure where a plurality of pixels are arranged at a predetermined pitch P, and which is addressed by electric signals representing information to be written, thereby modulating incident light; and an optically-addressed type spatial light modulator, which has an optical addressing layer and a light modulation layer between a pair of transparent electrodes and which modulates read light by the write light outputted from the electrically-addressed type spatial light modulator, an output end of the electrically-addressed type spatial light modulator, that faces the optically-addressed type spatial light modulator, being constructed from a light transmission layer with a uniform refractive index, a write light input end of the optically-addressed type spatial light modulator, that faces the electrically-addressed type spatial light modulator, being constructed from a fiber optical plate which has a refractive index distribution for transferring an input image while maintaining a resolution of the input image, the light transmission layer and the fiber optical plate being optically connected with each other, the optically-addressed type spatial light modulator having sensitivity characteristic to write light wavelength, the sensitivity characteristic having a predetermined sensitivity to a predetermined wavelength xcex and having another sensitivity to a wavelength other than the predetermined wavelength xcex, the predetermined sensitivity being higher than the other sensitivity, a numerical aperture NAFOP of the fiber optical plate, the predetermined pitch P of the pixel structure in the electrically-addressed type spatial light modulator, a thickness d of the light transmission layer, and a refractive index nG of the light transmission layer to the predetermined wavelength xcex satisfying the following relationship: NAFOP greater than nGxc2x7P/d.
According to the spatial light modulating device, with using no relay lens, the light transmission layer that constitutes the output end of the electrically-addressed type spatial light modulator is optically connected to the fiber optical plate that constitutes the write light input end of the optically-addressed type spatial light modulator. With this construction, write light is transmitted. In this case, by applying the condition NAFOP greater than nGxc2x7P/d to the numerical aperture NAFOP of the fiber optical plate for the predetermined wavelength xcex that mainly contributes to the modulation in the optically-addressed type spatial light modulator, it is possible to erase almost all the signal component that is caused by the pixel structure, similarly to the case where the relay lens is used. The predetermined frequency xcex may be a wavelength region having a predetermined wavelength width.
It is preferable that the numerical aperture NAFOP of the fiber optical plate, the predetermined pitch P of the pixel structure of the electrically-addressed type element, the thickness d of the light transmission layer, and the refractive index nG of the light transmission layer to the predetermined wavelength xcex further satisfy the following relationship: NAFOP less than 2nGxc2x7P/d. By further applying the condition of NAFOP less than 2nGxc2x7P/d to the numerical aperture NAFOP of the fiber optical plate for the wavelength xcex or wavelength region xcex that mainly -contributes to the modulation in the optically-addressed type spatial light modulator, it is possible to attain a spatial light modulating device that suffers from almost no degradation of the signal image, similarly to the case where the relay lens is used.
The electrically-addressed type spatial light modulator may preferably include a transmission type liquid crystal element. The optically-addressed type spatial light modulator may preferably include an optically-addressed type spatial light modulator that uses a photoconductive layer as the optical addressing layer and that uses a liquid crystal layer as the light modulation layer.
According to another aspect, a spatial light modulating device of the present invention comprises: a write light source for producing a write light; an electrically-addressed type element, which has a pixel structure where a plurality of pixels are arranged at a predetermined pitch P, which is addressed by electric signals representing information to be written, and which is inputted with the light from the write light source; a relay lens for transferring the write light which is generated by the electrically-addressed type element and which is outputted therefrom; an optically-addressed type spatial light modulator, which has an optical addressing layer and a light modulation layer between a pair of transparent electrodes; and a read light source for producing a read light for the optically-addressed type spatial light modulator, the relay lens having a numerical aperture NAL at a side of the electrically-addressed type element, the value of the numerical aperture NAL, the predetermined pitch P of the pixel structure of the electrically-addressed type element, and a wavelength xcex of the light from the write light source satisfying the following relationship: NAL/xcex less than 1/P.
By applying the condition of NAL/xcex less than 1/P to the numerical aperture of the relay lens, it is possible to erase, from write light that reaches the optically-addressed spatial light modulator, a signal component that is caused by the pixel structure of the electrically-addressed type element.
It is preferable that the value of the numerical aperture NAL, at the electrically-addressed type element side, of the relay lens, the predetermined pitch P of the pixel structure of the electrically-addressed type element, and the wavelength xcex of the light from the write light source further satisfy the following relationship: NAL/xcex greater than 1/2P. By further applying the condition of NAL/xcex greater than 1/2P to the numerical aperture of the relay lens, it is possible to transmit the write light without generating any degradation over the entire range of the spatial frequencies included in the signal image. It is therefore possible to attain a spatial light modulating device that can erase the signal component caused by the pixel structure and that can generate no degradation in the signal image.
It is preferable that the wavelength xcex of the light from the write light source has a wavelength width with a wavelength range of xcex1 less than xcex less than xcex2, the value of the numerical aperture NAL, at the electrically-addressed type element side, of the relay lens, the predetermined pitch P of the pixel structure of the electrically-addressed type element, and the wavelength range xcex1, xcex2 of the light from the write light source satisfying the following relationship: 1/2P less than NAL/xcex2, NAL/xcex1 less than 1/P.
It is preferable that the electrically-addressed type element includes a transmission type liquid crystal element. It is preferable that the optically-addressed type spatial light modulator includes an optically-addressed type spatial light modulator that uses a photoconductive layer as the optical addressing layer and that uses a liquid crystal layer as the light modulation layer.
According to still another aspect, a spatial light modulating device of the present invention comprises: a write light source for producing a write light; an electrically-addressed type element, which has a pixel structure where a plurality of pixels are arranged at a predetermined pitch P, which is addressed by electric signals representing information to be written, and which is inputted with the light from the write light source; an optically-addressed type spatial light modulator, which has an optical addressing layer and a light modulation layer between a pair of transparent electrodes; and a read light source for producing a read light for the optically-addressed type spatial light modulator, an output end of the electrically-addressed type element, that faces the optically-addressed type spatial light modulator, being constructed from a light transmission layer having a uniform refractive index, a write light input end of the optically-addressed type spatial light modulator, that faces the electrically-addressed type element, being constructed from a fiber optical plate which has a refractive index distribution for transferring an input image while maintaining a resolution of the input image, the light transmission layer and the fiber optical plate being optically connected with each other, a numerical aperture NAFOP of the fiber optical plate, the predetermined pitch P of the pixel structure of the electrically-addressed type element, a thickness d of the light transmission layer, and a refractive index nG of the light transmission layer to a wavelength xcex of the light from the write light source satisfying the following relationship: NAFOP greater than nGxc2x7P/d.
According to the spatial light modulating device, with using no relay lens, the light transmission layer that constitutes the output end of the electrically-addressed type element is optically connected to the fiber optical plate that constitutes the write light input end of the optically-addressed type spatial light modulator. With this construction, write light is transmitted. In this case, by applying the condition NAFOP greater than nGxc2x7P/d to the numerical aperture NAFOP of the fiber optical plate, it is possible to attain a spatial light modulating device that can erase a signal component caused by the pixel structure.
It is preferable that the numerical aperture NAFOP of the fiber optical plate, the predetermined pitch P of the pixel structure of the electrically-addressed type element, the thickness d of the light transmission layer, and the refractive index nG of the light transmission layer to the wavelength xcex of the light from the write light source further satisfy the following relationship: NAFOP less than 2nGxc2x7P/d.
By further applying the condition of NAFOP less than 2nGxc2x7P/d to the numerical aperture NAFOP of the fiber optical plate, it is possible to attain a spatial light modulating device that can erase a signal component caused by the pixel structure and that can generate no degradation in the signal image.
It is preferable that the electrically-addressed type element includes a transmission type liquid crystal element. It is preferable that the optically-addressed type spatial light modulator includes an optically-addressed type spatial light modulator that uses a photoconductive layer as the optical addressing layer and that uses a liquid crystal layer as the light modulation layer.
According to another aspect, a spatial light modulating method of the present invention comprises the steps of: addressing, by electric signals representing information to be written, an electrically-addressed type spatial light modulator, which has a pixel structure where a plurality of pixels are arranged at a predetermined pitch P; inputting a write light with a predetermined wavelength xcex to the electrically-addressed type spatial light modulator, and guiding the write light, which has been modulated by the electrically-addressed type spatial light modulator and which has been outputted therefrom, to an optical addressing layer of an optically-addressed type spatial light modulator via an optical connecting element having a critical transfer spatial frequency "ugr"c, the optically-addressed type spatial light modulator having the optical addressing layer and a light modulation layer between a pair of transparent electrodes; and inputting a read light to the light modulation layer of the optically-addressed type spatial light modulator, thereby allowing the read light to be modulated, the value of the critical transfer spatial frequency "ugr"c of the optical connecting element and the value of a pixel structure spatial frequency 1/P of the pixel structure in the electrically-addressed type spatial light modulator satisfying the following relationship: "ugr"c less than 1/P.
According to the spatial light modulating method described above, the relationship of "ugr"c less than 1/P is established between the critical transfer spatial frequency "ugr"c and the pixel structure spatial frequency 1/P. Accordingly, it is possible to erase, from write light that reaches the optically-addressed spatial light modulator, a signal component that is caused by the pixel structure of the electrically-addressed type spatial light modulator.
It is preferable that the value of the critical transfer spatial frequency "ugr"c, of the optical connecting element and the value of the pixel structure spatial frequency 1/P satisfy the following relationship: 1/2P less than "ugr"c. By further applying the condition of 1/2P less than "ugr"c to the critical transfer spatial frequency "ugr"c and the pixel structure spatial frequency 1/P, it is possible to transmit the write light without any degradation over the entire range of the spatial frequencies included in the signal image. It is therefore possible to attain a spatial light modulating method that can erase the signal component caused by the pixel structure and that can generate no degradation in the signal image.
It is preferable that the value of the critical transfer spatial frequency "ugr"c of the optical connecting element is determined based on a numerical aperture NA of the optical connecting element and the predetermined wavelength xcex.
It is preferable that the optical connecting element includes a relay lens that has a numerical aperture NAL at a side of the electrically-addressed type spatial light modulator, the value of the critical transfer spatial frequency "ugr"c being equal to NAL/xcex.
The optical connecting element may include a light transmission layer and a fiber optical plate which are connected with each other, the light transmission layer being connected to the electrically-addressed type spatial light modulator, the fiber optical plate being connected to the optically-addressed type spatial light modulator, the fiber optical plate having a numerical aperture NAFOP, the light transmission layer having a thickness d and having a predetermined refractive index nG to the predetermined wavelength xcex, the value of the critical transfer spatial frequency "ugr"c being substantially equal to nG/(dxc2x7NAFOP).
According to another aspect, a spatial light modulating method of the present invention comprises the steps of: addressing, by electric signals representing information to be written, an electrically-addressed type element, which has a pixel structure where a plurality of pixels are arranged at a predetermined pitch P; inputting a write light with a predetermined wavelength xcex to the electrically-addressed type element, and guiding the write light, which has been modulated by the electrically-addressed type element and which has been outputted therefrom, to an optical addressing layer of an optically-addressed type spatial light modulator via a relay lens having a numerical aperture NAL at a side of the electrically-addressed type element, the optically-addressed type spatial light modulator having the optical addressing layer and a light modulation layer between a pair of transparent electrodes; and inputting a read light to the light modulation layer of the optically-addressed type spatial light modulator, thereby allowing the read light to be modulated, the value of the numerical aperture NAL, at the side of the electrically-addressed type element, of the relay lens, the predetermined pitch P of the pixel structure of the electrically-addressed type element, and the wavelength xcex of the write light satisfying the following relationship: NAL/xcex less than 1/P.
According to the spatial light modulating method, by applying the condition of NAL/xcex less than 1/P to the numerical aperture of the relay lens, it is possible to erase, from write light that reaches the optically-addressed spatial light modulator, a signal component that is caused by the pixel structure of the electrically-addressed type element.
It is preferable that the value of the numerical aperture NAL, at the electrically-addressed type element side, of the relay lens, the predetermined pitch P of the pixel structure of the electrically-addressed type element, and the wavelength xcex of the light from the write light source further satisfy the following relationship: NAL/xcex greater than 1/2P. By further applying the condition of NAL/xcex greater than 1/2P to the numerical aperture of the relay lens, it is possible to transmit the write light without any degradation over the entire range of the spatial frequencies included in the signal image. It is therefore possible to attain a spatial light modulating method that can erase the signal component caused by the pixel structure and that can generate no degradation in the signal image.
It is preferable that the write light inputting step includes the step of inputting write light having a wavelength width with a wavelength range of xcex1 less than xcex less than xcex2 to the electrically-addressed type element, the value of the numerical aperture NAL, at the electrically-addressed type element side, of the relay lens, the predetermined pitch P of the pixel structure of the electrically-addressed type element, and the wavelength range xcex1, xcex2 of the write light satisfying the following relationship: 1/2P less than NAL/xcex2, NAL/xcex1 less than 1/P.
It is preferable that the electrically-addressed type element includes a transmission type liquid crystal element. It is preferable that the optically-addressed type spatial light modulator includes an optically-addressed type spatial light modulator that uses a photoconductive layer as the optical addressing layer and that uses a liquid crystal layer as the light modulation layer.
According to still another aspect, a spatial light modulating method of the present invention comprises the steps of: addressing, by electric signals representing information to be written, an electrically-addressed type element, which has a pixel structure where a plurality of pixels are arranged at a predetermined pitch P; inputting a write light with a predetermined wavelength xcex to the electrically-addressed type element, and guiding the write light, which has been modulated by the electrically-addressed type element and which has been outputted therefrom, to an optical addressing layer of an optically-addressed type spatial light modulator, via a light transmission layer, which has a thickness d and which has a refractive index nG to the predetermined wavelength xcex, and a fiber optical plate, which has a numerical aperture NAFOP, the optically-addressed type spatial light modulator having the optical addressing layer and a light modulation layer between a pair of transparent electrodes; and inputting a read light to the light modulation layer of the optically-addressed type spatial light modulator, thereby allowing the read light to be modulated, the numerical aperture NAFOP of the fiber optical plate, the predetermined pitch P of the pixel structure of the electrically-addressed type element, the thickness d of the light transmission layer, and the refractive index nG of the light transmission layer to the predetermined wavelength xcex of the write light satisfying the following relationship: NAFOP greater than nGxc2x7P/d.
According to the spatial light modulating method, with using no relay lens, the light transmission layer that constitutes the output end of the electrically-addressed type element is optically connected to the fiber optical plate that constitutes the write light input end of the optically-addressed type spatial light modulator. With this construction, write light is transmitted. In this case, by applying the condition NAFOP greater than nGxc2x7P/d to the numerical as aperture NAFOP of the fiber optical plate, it is possible to erase the signal component caused by the pixel structure, similarly to the case where the relay lens is used.
It is preferable that the numerical aperture NAFOP of the fiber optical plate, the predetermined pitch P of the pixel structure of the electrically-addressed type element, the thickness d of the light transmission layer, and the refractive index nG of the light transmission layer to the predetermined wavelength xcex of the write light further satisfy the following relationship: NAFOP less than 2nGxc2x7P/d. By further applying the condition of NAFOP less than 2nGxc2x7P/d to the numerical aperture NAFOP of the fiber optical plate, it is possible to attain a spatial light modulating method that can erase the signal component caused by the pixel structure and that suffers from no degradation of the signal image.
It is preferable that the electrically-addressed type element includes a transmission type liquid crystal element. It is preferable that the optically-addressed type spatial light modulator includes an optically-addressed type spatial light modulator that uses a photoconductive layer as the optical addressing layer and that uses a liquid crystal layer as the light modulation layer.